Interference-resilient transceivers, where the receiver (RX) is able to operate without performance degradation under a large interference power, are often required in many applications including full-duplex wireless communication, magnetic resonance and dielectric spectroscopy, and full-duplex radar. Existing interference-resilient transceivers can be characterized into two categories: (1) Reject the interference at IF with little voltage gain at RF (mixer-first). (2) Reject the interference at RF using a high-Q filter. Unfortunately, method 1 suffers from large 1/f noise contributed by mixers and baseband circuitries at low IF due to the lack of voltage gain at RF. While method 2 has a low interference P1 dB when the frequency offset between the interference and desired RX signal is small due to the low quality factor of the RF filter. Thus, method 2 is limited by the filter quality factor.
Recently, Electron Paramagnetic Resonance (EPR) spectroscopy has attracted great interest from both academia and industry. It is in concept highly similar to nuclear magnetic resonance (NMR), except that EPR spectroscopy detects magnetic moments generated by unpaired electrons instead of nucleus. EPR spectroscopy has a broad range of applications, such as discussed in WO 2015/048249 filed Sep. 25, 2014, US2014/0091802 filed Sep. 30, 2013, and 2014/0097842 filed Sep. 30, 2013.
In EPR spectroscopy, there is a desire for low NF at low IF. TX and RX may operate at the same time, where TX operates at fTX of several to tens of GHz. TX leakage power may easily reach −10 dBm. RX may operate at fTX±fM, where fM is tens of kHz. The interference is caused by the power leakage from the transmitter (TX) (self-interference), which may operate at GHz frequencies, and can easily reach −10 dBm. Moreover, the frequency offset between the TX and the desired RX signal, as well as the frequency of the IF signal, may be less than 100 kHz. Under such stringent conditions, existing interference-resilient architectures cannot satisfy both noise and linearity requirements, simultaneously. As a result, conventional high-performance EPR spectrometers may separate the TX and RX into dedicated discrete components that are bulky and costly.
An active cancellation structure is discussed herein that improves sensitivity of EPR systems or the like.